That’s two more than the airline found by Monday afternoon. Southwest said operations were returning to normal after nearly 700 flights were canceled Saturday through Monday. Southwest grounded 79 older Boeing 737-300 planes after a similar jet sprang a hole in the roof Friday on a flight from Phoenix.

Federal officials say they will order emergency inspections of some older 737s for cracks in the fuselage like the ones on the Southwest jets. The Federal Aviation Administration order was expected on Tuesday.

Southwest said it had already complied with the new order by grounding and inspecting planes over the weekend. The airline said the five planes with “minor subsurface cracking” will remain grounded until Boeing recommends a process for repairing them and the airline completes the work.

This is a typical failure that could have bee prevented. I have some questions:
Is the fuselage sheet metal the right material for the job? Does it has the right temper? Does it complies with all the mechanical properties? There’s more question that can be asked. What needs to be made public is what is the root cause of the problem.